Anterior cruciate ligament substituting knee implants

ABSTRACT

The present disclosure provides knee prostheses that replicate at least a portion of the function of an individual patient&#39;s anterior cruciate ligament (ACL). An exemplary knee prosthesis includes a femoral component configured to be implanted on the distal end of the patient&#39;s femur and a tibial component configured to be implanted on the proximal end of the patient&#39;s tibia. In extension, the femoral component and the tibial component may cooperate to limit anterior movement of the tibial component relative to the femoral component. In flexion, the femoral component may be free to rotate relative to the tibial component.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/086,104, filed on 13 Apr. 2011, now U.S. Pat. No. 9,132,014, whichapplication claims priority from U.S. Provisional Patent ApplicationSer. No. 61/323,380, entitled “Anterior Cruciate Substituting KneeImplants,” filed Apr. 13, 2010, the disclosures of which are herebyexpressly incorporated by reference herein in their entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to prosthetic implants and, specifically,to anterior cruciate ligament substituting knee implants.

BACKGROUND OF THE DISCLOSURE

In a natural knee joint, the distal end of the femur articulates againstthe proximal end of the tibia. The knee joint is supported by variousligaments, including the posterior cruciate ligament (PCL) and theanterior cruciate ligament (ACL). These ligaments stabilize the kneejoint while at rest in full extension. Also, these ligaments cooperateto control the complex movements of the knee joint during flexion andextension. The PCL originates medially on the distal femur and attachesto the posterior side of the proximal tibia to resist posteriortranslation of the tibia relative to the femur. The ACL, on the otherhand, originates at the distal femur and attaches to the anterior sideof the proximal tibia to resist anterior translation of the tibiarelative to the femur.

During flexion and extension of the knee joint, the ligaments of theknee joint work in concert with the meniscus and the geometry of thefemur and tibia to effect rotation of the femur about an axis that isoffset in a medial direction relative to the center of the knee joint.As a result, the lateral femoral condyle travels along an arcuate pathacross the proximal tibia, while the medial femoral condyle maintains arelatively central position on the proximal tibia.

Referring to FIGS. 1-7, a natural knee joint is shown in various degreesof flexion and extension.

The knee joint is shown in full extension in FIGS. 1-3. When the kneejoint is in extension, femur 10 and tibia 12 are aligned such that, fromthe side view of FIG. 1, femur 10 and tibia 12 extend along asubstantially straight line. In this position, medial and lateralcondyles 14, 16, of femur 10 are positioned atop medial and lateralportions 18, 20, of tibial plateau 22, respectively. Ovals 28, 30, ofFIG. 2 depict the contact area of medial and lateral femoral condyles14, 16, respectively, upon tibial plateau 22. As shown, contact areas28, 30, of medial and lateral femoral condyles 14, 16, are generallycentered atop tibial plateau 22. Contact areas 28, 30, of medial andlateral femoral condyles 14, 16, have sufficient length L and width W toprovide stability to the knee joint when in extension. Additionally, asshown in FIG. 3, intercondylar eminence 24 of tibial plateau 22 extendsproximally into intercondylar notch 26 of femur 10 to provide additionalstability to the knee joint. In this position, the ACL (not shown)resists anterior translation of the tibia 12 relative to the femur 10.

The knee joint is shown in mid-flexion in FIGS. 4 and 5. Specifically,the knee joint is bent such that femur 10 is rotated relative to tibia12 by approximately 45°. As the knee joint moves into mid-flexion, thefemur 10 rotates about an axis A that is medially offset from acenterline of the knee joint. Therefore, contact area 30′ of lateralfemoral condyle 16 advances posteriorly from full extension tomid-flexion, as shown in FIG. 5 by comparing the contact area 30 in fullextension (shown in phantom) with the contact area 30′ in mid-flexion(shown in solid lines). Also, contact area 30′ of lateral femoralcondyle 16 advances posteriorly relative to contact area 28′ of medialfemoral condyle 14. Additionally, as the knee joint moves intomid-flexion, contact areas 28′, 30′, decrease in length L′ and width W′,because the radius of curvature of medial and lateral femoral condyles14, 16, decreases posteriorly both in a plane parallel to a sagittalplane (e.g., along length L) and in a coronal plane (e.g., along widthW).

The knee joint is shown in a state of increased flexion in FIGS. 6 and7. Specifically, the knee joint is bent such that femur 10 is rotatedrelative to tibia 12 by another 45°, with femur 10 and tibia 12 formingan angle of approximately 90° therebetween. As the knee joint continuesto bend, the femur 10 continues to rotate about axis A. Therefore,contact area 30″ of lateral femoral condyle 16 advances posteriorly frommid-flexion to full flexion, as shown in FIG. 7 by comparing the contactarea 30′ in mid-flexion (shown in phantom) with the contact area 30″ infull flexion (shown in solid lines). Additionally, as the knee jointcontinues to bend, contact areas 28 ″, 30 ″, decrease further in lengthL″ and width W″. The reduced size of contact areas 28 ″, 30 ″, eases theability for femur 10 to rotate relative to tibia 12 about axis A.

Because the lateral femoral condyle 16 travels further across tibialplateau 22 than medial femoral condyle 14, tibia 12 rotates relative tofemur 10 during flexion and extension. As the knee joint flexes fromfull extension (FIG. 2) to mid-extension (FIG. 5), tibia 12 rotatesinternally relative to femur 10. Conversely, as the knee joint extendsfrom mid-extension (FIG. 5) to full extension (FIG. 2), tibia 12 rotatesexternally relative to femur 10. This external rotation of tibia 12tightens the ligaments of the knee joint and “locks” the knee jointagainst further rotation to stabilize the knee joint in full extension.This behavior of the knee joint when reaching full extension is known asthe “screw home mechanism.”

When a normal knee joint becomes damaged and knee arthroplasty isrequired, it may be necessary to sacrifice ligaments of the knee joint,including the ACL. However, without the ACL, it may be difficult torecreate the stability and the complex movements of the natural kneejoint. For example, without the ACL, the tibia may translate anteriorlyrelative to the femur. Also, without the ACL, the lateral femoralcondyle may not rotate about a medially offset axis.

SUMMARY OF THE DISCLOSURE

The present disclosure provides knee prostheses that replicate at leasta portion of the function of an individual patient's anterior cruciateligament (ACL). The knee prostheses of the present disclosure may alsoaccommodate a healthy, functional posterior cruciate ligament (PCL). Anexemplary knee prosthesis includes a femoral component configured to beimplanted on the distal end of the patient's femur and a tibialcomponent configured to be implanted on the proximal end of thepatient's tibia. In extension, the femoral component and the tibialcomponent may cooperate to limit anterior movement of the tibialcomponent relative to the femoral component. In flexion, the femoralcomponent may be free to translate and/or rotate relative to the tibialcomponent.

According to an exemplary embodiment of the present disclosure, a kneeprosthesis is provided that articulates between a substantially extendedposition and a flexed position. The knee prosthesis includes an axisthat is medially offset from a center of the knee prosthesis. The kneeprosthesis further includes a femoral component including a medialcondyle and a lateral condyle and a tibial component including a medialsurface sized to receive the medial condyle of the femoral component anda lateral surface sized to receive the lateral condyle of the femoralcomponent. The femoral and tibial components are more constrainedagainst at least one of the following movements when the knee prosthesisis in the substantially extended position than when the knee prosthesisis in the flexed position: a rotational movement of the femoralcomponent relative to the tibial component about the axis; an anteriormovement of the tibial component relative to the femoral component; anda lateral movement of the femoral component relative to the tibialcomponent, whereby the knee prosthesis resists at least one of therotational movement and the anterior movement to a greater extent whenthe knee prosthesis is in the substantially extended position than whenthe knee prosthesis is in the flexed position.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a lateral, elevational view of a left knee joint in fullextension, the knee joint formed between a femur and a tibia;

FIG. 2 is a plan view of the tibia of FIG. 1 depicting the area ofcontact between the tibia and the femur in full extension;

FIG. 3 is an anterior, elevational view of the knee joint of FIG. 1;

FIG. 4 is a lateral, elevational view of the knee joint of FIG. 1 inearly flexion;

FIG. 5 is a plan view of the tibia of FIG. 4 depicting the area ofcontact between the tibia and the femur in early flexion;

FIG. 6 is a lateral, elevational view of the knee joint of FIG. 1 in astate of further flexion;

FIG. 7 is a plan view of the tibia of FIG. 6 depicting the area ofcontact between the tibia and the femur in the state of further flexion;

FIG. 8 is a cross-sectional view of an exemplary knee prosthesis in fullextension, the knee prosthesis including a femoral component and atibial component;

FIG. 9 is a plan view of the tibial component of FIG. 8 depicting thearea of contact between the tibial component and the femoral componentin full extension;

FIG. 10 is a view similar to FIG. 8 showing the knee prosthesis in earlyflexion;

FIG. 11 is a plan view of the tibial component of FIG. 10 depicting thearea of contact between the tibial component and the femoral componentin early flexion;

FIG. 12 is a view similar to FIG. 10 showing the knee prosthesis in astate of further flexion;

FIG. 13 is a plan view of the tibial component of FIG. 12 depicting thearea of contact between the tibial component and the femoral componentin the state of further flexion;

FIG. 14 is a cross-sectional view of another exemplary knee prosthesisin full extension;

FIG. 15 is a partial, cross-sectional view of the knee prosthesis ofFIG. 14, taken along line 15-15 of FIG. 14;

FIG. 16 is a view similar to FIG. 14 showing the knee prosthesis inearly flexion;

FIG. 17 is a partial, cross-sectional view of the knee prosthesis ofFIG. 16, taken along line 17-17 of FIG. 16;

FIG. 18 is a cross-sectional view of another exemplary knee prosthesisin full extension;

FIG. 18A is a partial, cross-sectional view of the knee prosthesis ofFIG. 18, taken along line 18A-18A of FIG. 18;

FIG. 19 is a view similar to FIG. 18 showing the knee prosthesis inearly flexion;

FIG. 19A is a partial, cross-sectional view of the knee prosthesis ofFIG. 19, taken along line 19A-19A of FIG. 19;

FIG. 20 is a cross-sectional view of yet another exemplary kneeprosthesis in full extension;

FIG. 21 is a view similar to FIG. 20 showing the knee prosthesis inearly flexion;

FIG. 22 is a cross-sectional view of yet another exemplary kneeprosthesis in full extension;

FIG. 23 is a view similar to FIG. 22 showing the knee prosthesis inearly flexion;

FIG. 24 is a view similar to FIG. 23 showing the knee prosthesis in astate of further flexion;

FIG. 25 is a medial cross-sectional view of yet another exemplary kneeprosthesis in full extension;

FIG. 26 is a view similar to FIG. 25 showing the knee prosthesis inearly flexion;

FIG. 27 is a lateral cross-sectional view of the knee prosthesis of FIG.25;

FIG. 28 is a view similar to FIG. 27 showing the knee prosthesis inearly flexion;

FIG. 29 is a plan view of a tibial component of yet another exemplaryknee prosthesis;

FIG. 30 is a partial, cross-sectional view of the tibial component ofFIG. 29, taken along line 30-30 of FIG. 29, the knee prosthesisincluding a femoral component in early flexion relative to the tibialcomponent;

FIG. 31 is a view similar to FIG. 30 showing the knee prosthesis in fullextension, taken along line 31-31 of FIG. 29;

FIG. 32 is a plan view of a tibial component of yet another exemplaryknee prosthesis;

FIG. 33 is a cross-sectional view of the tibial component of FIG. 32,taken along line 33-33 of FIG. 32;

FIG. 34 is a medial, elevational view of a femoral component for use inconjunction with the tibial component of FIG. 32;

FIG. 35 is a cross-sectional view of the femoral component of FIG. 34,taken along line 35-35 of FIG. 34;

FIG. 36 is a cross-sectional view of the femoral component of FIG. 34,taken along line 36-36 of FIG. 34;

FIG. 37 is a cross-sectional view of the femoral component of FIG. 34.taken along line 37-37 of FIG. 34;

FIG. 38 is a cross-sectional view of still yet another exemplary kneeprosthesis in full extension;

FIG. 39 is a view similar to FIG. 38 showing the knee prosthesis inearly flexion;

FIG. 40 is a plan view of a tibial component of yet another exemplaryknee prosthesis;

FIG. 41 is a cross-sectional view of a femoral component for use inconjunction with the tibial component of FIG. 40;

FIG. 42 is a cross-sectional view of the tibial component of FIG. 40,taken along line 42-42 of FIG. 40, and the femoral component of FIG. 41,taken along line 42-42 of FIG. 41;

FIG. 42A is an alternative cross-sectional view of the tibial componentof FIG. 40, taken along line 42-42 of FIG. 40;

FIG. 43 is a cross-sectional view of the tibial component of FIG. 40,taken along line 43-43 of FIG. 40;

FIG. 44 is a cross-sectional view of the tibial component of FIG. 40,taken along line 44-44 of FIG. 40;

FIG. 45 is a cross-sectional view of still yet another exemplary kneeprosthesis in full extension;

FIG. 46 is a view similar to FIG. 45 showing the knee prosthesis inearly flexion;

FIG. 47 is a lateral, elevational view of still yet another exemplaryknee prosthesis in full extension, the knee prosthesis including afemoral component and a tibial component;

FIG. 48 is a partial cross-sectional view of the knee prosthesis of FIG.47, taken along line 48-48 of FIG. 47;

FIG. 49 is a top plan view of the tibial component of FIG. 47, takenalong line 49-49 of FIG. 47;

FIG. 50 is a bottom plan view of the femoral component of FIG. 47, takenalong line 50-50 of FIG. 47;

FIG. 51 is a lateral, elevational view of still yet another exemplaryknee prosthesis in full extension, the knee prosthesis including afemoral component and a tibial component;

FIG. 52 is a top plan view of the tibial component of FIG. 51, takenalong line 52-52 of FIG. 51;

FIG. 53 is a bottom plan view of the femoral prosthesis of FIG. 51,taken along line 53-53 of FIG. 51;

FIG. 54 is a medial cross-sectional view of still yet another exemplaryknee prosthesis in full extension;

FIG. 55 is a view similar to FIG. 54 showing the knee prosthesis inearly flexion;

FIG. 56 is a top plan view of still yet another exemplary kneeprosthesis in full extension; and

FIG. 57 is a top plan view of the knee prosthesis of FIG. 56 in earlyflexion.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate preferred embodiments of the invention and suchexemplifications are not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION

As discussed above with respect to FIGS. 1-7, the natural knee joint issupported by various ligaments, including the posterior cruciateligament (PCL) and the anterior cruciate ligament (ACL). These ligamentswork in concert with the meniscus and the geometry of the femur andtibia to effect rotation of femur 10 about a medially offset axis Arelative to tibia 12. Also, the ACL, in particular, resists anteriortranslation of tibia 12 relative to the femur 10.

In certain cases, the ACL must be sacrificed. The knee joint prosthesesof the present disclosure function to replicate at least one of thebeneficial aspects of the ACL. When the knee joint is located in fullextension or somewhere between full extension and early flexion (alsoreferred to herein as “substantially extended positions”), the kneejoint prostheses of the present disclosure may be arranged in a firstconfiguration that is more restricted to movement. For example, the kneejoint prostheses of the present disclosure may resist anteriortranslation of tibia 12 relative to the femur 10 in the firstconfiguration. As another example, the knee joint prostheses of thepresent disclosure may limit rotation of tibia 12 relative to femur 10in the first configuration. However, when the knee joint flexes beyondearly flexion, the knee joint prostheses of the present disclosure maybe arranged in a second configuration that is less restricted tomovement.

The point at which the knee joint prosthesis transitions from the first,more restricted configuration to the second, less restrictedconfiguration may vary depending on the needs of particular patients.For example, in certain embodiments, the knee joint prosthesis may enterthe second, less restricted configuration at approximately 10°, 20°, or30° of knee flexion (i.e., early flexion), such that the knee jointprosthesis is arranged in the first, more restricted configuration inthe substantially extended positions of 0° of knee flexion (i.e., fullextension) up to approximately 10°, 20°, or 30° of knee flexion (i.e.,early flexion). It is within the scope of the present disclosure thatthe transition from the first configuration to the second configurationmay occur gradually, such as over 5°, 10°, or more, of knee flexion.

Referring to FIGS. 8-13, an exemplary knee prosthesis 40 is shown. Kneeprosthesis 40 includes femoral component 42 and tibial component 44.Femoral component 42 and tibial component 44 are implanted onto femur 10and tibia 12, respectively, in a known manner.

Femoral component 42 of knee prosthesis 40 includes an anteriorpatello-femoral flange 46, medial condyle 48, and an opposing lateralcondyle (not shown). Optionally, femoral component 42 may also includecrossbar 50. Crossbar 50 extends between medial condyle 48 and theopposing lateral condyle of femoral component 42. Crossbar 50 is spacedapart from the distal-most end 52 of patello-femoral flange 46 andcooperates with patello-femoral flange 46 to define opening 54therebetween. As shown in FIG. 8, opening 54 is sized for receipt ofprojection 56 therein, which extends proximally from tibial component44. In one exemplary embodiment, the distal-most end 52 ofpatello-femoral flange 46 and/or distal wall 66 of crossbar 50 areslanted distally in an anterior-posterior direction to define afunnel-shaped opening 54 therebetween.

Tibial component 44 of knee prosthesis is shown in FIG. 9. Tibialcomponent 44 includes medial articulating surface 58 and lateralarticulating surface 60. Medial and lateral articulating surfaces 58,60, are formed in a traditional manner as generally concave surfaces.Projection 56 is positioned between medial and lateral articulatingsurfaces 58, 60, of tibial component 44 and extends proximally andslightly posteriorly from the proximal surface of tibial component 44.In one exemplary embodiment, projection 56 terminates proximally atcurved end 62 and includes partially curved anterior wall 64. Toaccommodate the patient's PCL, tibial component 44 may include posteriorcutout 68.

With the knee joint in extension, as shown in FIGS. 8 and 9, projection56 of tibial component 44 is received within opening 54 of femoralcomponent 42. If tibia 12 were forced anteriorly relative to femur 10 inthis extended position, anterior wall 64 of projection 56 would abut thedistal-most end 52 of patello-femoral flange 46 to limit anteriormovement of tibia 12 relative to femur 10. Also, if tibia 12 were forcedposteriorly relative to femur 10 in this extended position, projection56 would abut crossbar 50 to limit posterior movement of tibia 12relative to femur 10.

As the knee joint reaches early flexion, as shown in FIGS. 10 and 11,the curved proximal end 62 of projection 56 may slide across theslanted, distal wall 66 of crossbar 50. By maintaining contact betweenprojection 56 and crossbar 50 during early flexion, femur 10 isprevented from sliding anteriorly relative to tibia 12, and tibia 12 isprevented from sliding posteriorly relative to femur 10.

In an exemplary embodiment, patello-femoral flange 46, projection 56,and/or crossbar 50 may interact to drive rotation of femoral component42 relative to tibial component 44 about a medially offset axis A. Forexample, the shape and/or orientation of patello-femoral flange 46,crossbar 50, and/or projection 56 may vary in a medial-lateral directionto force the lateral condyle (not shown) of femoral component 42 torotate about axis A. As a result, during flexion of the knee joint,contact area 47′ of the lateral condyle of femoral component 42 advancesposteriorly from full extension to early flexion, as shown in FIG. 11 bycomparing the contact area 47 in full extension (shown in phantom) withthe contact area 47′ in early flexion (shown in solid lines). Bymodifying the shape and/or orientation of patello-femoral flange 46,crossbar 50, and/or projection 56, the rotation and posterior movementof femoral component 42 and tibial component 44 relative to one anothercan be correspondingly modified.

As the knee joint enters a deeper state of flexion, as shown in FIGS. 12and 13, projection 56 may be freed from opening 54 between crossbar 50and patello-femoral flange 46. In this flexed position, projection 56may no longer contact crossbar 50. Once projection 56 is freed fromopening 54, the relative movement between femoral component 42 andtibial component 44 becomes uninhibited. Therefore, in one exemplaryembodiment, femoral component 42 may be free to rotate naturally aboutaxis A relative to tibial component 44. Alternatively, in anotherexemplary embodiment, knee prosthesis 40 may incorporate some of theadditional concepts disclosed herein to continue to drive rotation offemoral component 42 relative to tibial component 44 about axis A.

As the knee joint returns to extension, as shown in FIG. 8, curvedproximal end 62 of projection 56 may slide back across the slanted,distal-most end 52 of patello-femoral flange 46 and/or the slanted,distal wall 66 of crossbar 50. Then, once curved proximal end 62 ofprojection 56 reaches the end of the distal-most end 52 ofpatello-femoral flange 46 and/or the distal wall 66 of crossbar 50,femoral component 42 may snap back into place atop tibial component 44.As discussed above, opening 54 may be funnel-shaped (i.e., wider at itsdistal end than at its proximal end) so that projection 56 is encouragedto find and enter the distal end of opening 54 as the knee joint returnsto extension. As projection 56 moves toward the proximal end of opening54, the narrowing of opening 54 helps maintain tibial component 44 inplace relative to femoral component 42.

Another exemplary knee prosthesis 40′ is shown in FIGS. 56 and 57, withknee prosthesis 40′ being similar to knee prosthesis 40 of FIGS. 8-13and with like reference numerals identifying like elements. Theillustrative crossbar 50′ of knee prosthesis 40′ extends along axis C′,which deviates from medial-lateral axis ML′. With the knee joint inextension, as shown in FIG. 56, projection 56′ abuts patello-femoralflange 46′ to screw home and lock femoral component 42′ in internalrotation relative to tibial component 44′. With the knee joint in earlyflexion, as shown in FIG. 57, femoral component 42′ is able to rotaterelative to tibial component 44′ about the medially offset axis A′. Asfemoral component 42′ rotates, projection 56′ substantially disengagesthe patello-femoral flange 46′ and instead abuts crossbar 50′. As theknee joint enters a deeper state of flexion, projection 56′ may beentirely freed from opening 54′ between patello-femoral flange 46′ andcrossbar 50′ (See, e.g., FIG. 12). As discussed above with respect toknee prosthesis 40 of FIGS. 8-13, it is also within the scope of thepresent disclosure that the shape and/or orientation of patello-femoralflange 46′ and/or projection 56′ may vary in addition to or instead ofcrossbar 50′.

Referring next to FIGS. 14-17, another exemplary knee prosthesis 70 isshown. Knee prosthesis 70 includes femoral component 72 and tibialcomponent 74. Femoral component 72 and tibial component 74 are implantedonto femur 10 and tibia 12, respectively, in a known manner. Kneeprosthesis 70 may incorporate features of knee prosthesis 40 of FIGS.8-13 and/or knee prosthesis 40′ of FIGS. 56 and 57.

Tibial component 74 of knee prosthesis 70 may be formed in a traditionalmanner and includes medial and lateral articulating surfaces 76, 78, andtibial eminence 80 located therebetween. Femoral component 72 of kneeprosthesis 70 may also be formed in a traditional manner and includes ananterior patello-femoral flange 82 and medial and lateral condyles 84,86, respectively. However, unlike known femoral prostheses, medial andlateral condyles 84, 86, of femoral component 72 have, in a posteriordirection, a progressively decreasing width and a progressivelydecreasing medial-lateral radius of curvature.

With the knee joint in extension, as shown in FIGS. 14 and 15, theportion of medial and lateral condyles 84, 86, of femoral component 72that contacts medial and lateral articulating surfaces 76, 78, of tibialcomponent 74 (i.e., the portion intersected by line 15-15 in FIG. 14)has a relatively large medial-lateral radius of curvature R and arelatively large width W. Therefore, as shown in FIG. 15, medial andlateral condyles 84, 86, of femoral component 72 substantially match themedial-lateral curvature of medial and lateral articulating surfaces 76,78, of tibial component 74. Also, medial and lateral condyles 84, 86, offemoral component 72 extend substantially entirely across medial andlateral articulating surfaces 76, 78, of tibial component 74. In thisextended position, the close, constrained fit between femoral component72 and tibial component 74 prevents relative rotation between thecomponents.

With the knee joint in flexion, as shown in FIGS. 16 and 17, the portionof medial and lateral condyles 84, 86, of femoral component 72 thatcontacts medial and lateral articulating surfaces 76, 78, of tibialcomponent 74 (i.e., the portion intersected by line 17-17 in FIG. 16)has a relatively small medial-lateral radius of curvature R′ (i.e., lessthan radius R) and a relatively small width W′ (i.e., less than widthW). Therefore, the contact area between femoral component 72 and tibialcomponent 74 decreases from the extended position (FIG. 15) to theflexed position (FIG. 17). In the flexed position, the loose fit betweenfemoral component 72 and tibial component 74 enables relative rotationbetween femoral component 72 and tibial component 74. For example,femoral component 72 may be free to rotate relative to tibial component74 about axis A without impinging upon tibial eminence 80. Rather thanchanging the size or shape of both medial and lateral condyles 84, 86,it is also within the scope of the present disclosure that only onecondyle, such as lateral condyle 86, may change size or shape. In thisembodiment, medial condyle 84 may maintain close conformity with tibialcomponent 74 to produce a medial camming action, while lateral condyle86 may decrease in width W′ and/or medial-lateral curvature R′ toachieve a loose fit with tibial component 74 and to enable rotationabout axis A.

Beyond the flexed position of FIGS. 16 and 17, medial and lateralcondyles 84, 86, of femoral component 72 may continue to decrease inwidth and medial-lateral curvature. Therefore, as femoral component 72continues to bend posteriorly relative to tibial component 74, rotatingfemoral component 72 relative to tibial component 74 about axis A maybecome progressively easier.

Referring next to FIGS. 18-19, yet another exemplary knee prosthesis 90is shown. Knee prosthesis 90 includes femoral component 98 and tibialcomponent 92. Femoral component 98 and tibial component 92 are implantedonto femur 10 and tibia 12, respectively, in a known manner. Kneeprosthesis 90 may incorporate features of knee prosthesis 40 of FIGS.8-13, knee prosthesis 40′ of FIGS. 56 and 57, and/or knee prosthesis 70of FIGS. 14-17.

Femoral component 98 of knee prosthesis 40 includes an anteriorpatello-femoral flange 96, medial condyle 93, and an opposing lateralcondyle 91. Patello-femoral flange 96 includes a distal-most end 95.

Tibial component 92 of knee prosthesis 90 includes projection 94 thatextends proximally from the medial-lateral midpoint of tibial component92, as shown in FIG. 18A. Projection 94 includes anterior wall 97. Asshown in FIG. 18, projection 94 is spaced slightly anteriorly of theanterior-posterior midpoint of tibial component 92. Because projection94 terminates before reaching the posterior-most end of tibial component92, projection 94 may avoid interfering with a patient's PCL.

With the knee joint in extension, as shown in FIGS. 18 and 18A, anteriorwall 97 of projection 94 abuts the distal-most end 95 of patello-femoralflange 96 to limit anterior movement of tibia 12 relative to femur 10.Also, projection 94 extends between medial and lateral femoral condyles93, 91, to limit rotational movement of femoral component 98 relative totibial component 92.

With the knee joint in flexion, as shown in FIGS. 19 and 19A, thedistal-most end 95 of patello-femoral flange 96 may disengage anteriorwall 97 of projection 94. Also, femoral component 98 may translateposteriorly behind protrusion 94, allowing femoral component 98 torotate naturally relative to tibial component 92 about axis A withoutsubstantially impeding upon protrusion 94.

Referring next to FIGS. 20 and 21, yet another exemplary knee prosthesis110 is shown. Knee prosthesis 110 includes femoral component 112 andtibial component 114. Femoral component 112 and tibial component 114 areimplanted onto femur 10 and tibia 12, respectively, in a known manner.Knee prosthesis 110 may incorporate features of knee prosthesis 40 ofFIGS. 8-13, knee prosthesis 40′ of FIGS. 56 and 57, knee prosthesis 70of FIGS. 14-17, and/or knee prosthesis 90 of FIGS. 18-19.

Lateral condyle 116 of femoral component 112 includes projection 118having arcuate end 120 that extends distally from lateral condyle 116.Lateral articulating surface 124 of tibial component 114 includes acorresponding recess or opening 122 that is sized to receive projection118 from femoral component 112. As shown in FIG. 20, opening 122 isdefined by posterior wall 126 and ramped surface 128 of tibial component114. In certain embodiments, projection 118 and opening 122 may beformed at the outermost, lateral edge of femoral component 112 andtibial component 114. It is within the scope of the present disclosurethat a similar projection 118 and a corresponding opening 122 may beformed on a medial condyle (not shown) of femoral component 112 and amedial articulating surface (not shown) of tibial component 114, insteadof or in addition to those features formed on lateral condyle 116 andlateral articulating surface 124.

With the knee joint in extension, as shown in FIG. 20, posterior wall126 of opening 122 in tibial component 114 abuts projection 118 offemoral component 112 to limit anterior movement of tibia 12 relative tofemur 10. Then, as the knee enters a state of flexion, as shown in FIG.21, projection 118 travels along ramped surface 128 to exit opening 122.Once in this flexed position, femoral component 112 and tibial component114 may move relative to one another in a natural, unobstructed manner.

Referring next to FIGS. 22-24, an alternative embodiment knee prosthesis110′ is shown. Unlike opening 122 of knee prosthesis 110 which includesramped surface 128 (FIGS. 20-21), opening 130 of knee prosthesis 110′lacks a ramped surface. In this embodiment, opening 130 includesopposing sidewalls 132, 134, that cooperate to define opening 130.

With the knee joint in extension, as shown in FIG. 20, sidewalls 132,134, of tibial component 114′ abut projection 118′ of femoral component112′ to limit anterior and posterior movement of tibia 12 relative tofemur 10. As the knee joint begins to enter a state of flexion, as shownin FIG. 23, projection 118′ contacts anterior wall 132 of tibialcomponent 114′, which may force lateral condyle 116′ of femoralcomponent 112′ in a posterior direction to a greater extent that themedial condyle (not shown) of femoral component 112′. Therefore,anterior wall 132 of tibial component 114′ may drive rotation of femoralcomponent 112′. As the knee joint continues to bend, as shown in FIG.24, projection 118′ may withdraw from opening 130 and, as a result,femoral component 112′ and tibial component 114′ may move relative toone another in a natural, unobstructed manner. Although projection 118′is described as being formed on lateral condyle 116′ of femoralcomponent 112′ to induce translation and/or rotation of lateral condyle116′, it is also within the scope of the present disclosure thatprojection 118′ may be formed on a medial condyle (not shown) of femoralcomponent 112′, instead of or in addition to lateral condyle 116′. Ineither location, projection 118′ may encourage anterior movement offemoral component 112′ when the knee joint transitions from flexion(FIG. 24) to extension (FIG. 22).

Referring to FIGS. 25-28, yet another exemplary knee prosthesis 140 isshown. Knee prosthesis 140 includes femoral component 142 and tibialcomponent 144, which may be a mobile bearing tibial component. Femoralcomponent 142 and tibial component 144 are implanted onto femur 10 andtibia 12, respectively, in a known manner. Knee prosthesis 140 mayincorporate features of knee prosthesis 40 of FIGS. 8-13, kneeprosthesis 40′ of FIGS. 56 and 57, knee prosthesis 70 of FIGS. 14-17,knee prosthesis 90 of FIGS. 18-19, knee prosthesis 110 of FIGS. 20 and21, and/or knee prosthesis 110′ of FIGS. 22-24.

The medial side of knee prosthesis 140 is shown in FIGS. 25 and 26.Specifically, the medial side of knee prosthesis 140 includes medialcondyle 146 of femoral component 142 and medial articulating surface 148of tibial component 144. The medial side of knee prosthesis 140 may bein the shape of a traditional cruciate-retaining prosthesis.

The lateral side of knee prosthesis 140 is shown in FIGS. 27 and 28.Specifically, the lateral side of knee prosthesis 140 includes lateralcondyle 150 of femoral component 142 and lateral articulating surface152 of tibial component 144.

The lateral side of knee prosthesis 140 differs from the medial side ofknee prosthesis 140. Specifically, lateral articulating surface 152 oftibial component 144 includes a first, anterior section 154 and asecond, posterior section 156 separated by inflection point 158. In oneexemplary embodiment, both anterior portion 154 and posterior portion156 define substantially concave articulating surfaces. In anotherexemplary embodiment, anterior portion 154 defines a substantiallyconcave or flat articulating surface, while posterior portion 156defines a ramped articulating surface.

When the knee joint is in extension, as shown in FIG. 27, lateralcondyle 150 of femoral component 142 may conform to the shape ofanterior portion 154 of lateral articulating surface 152. For example,anterior portion 154 of lateral articulating surface 152 may define aconcave pocket that cradles lateral condyle 150 of femoral component142. Femoral component 142 will be held in this extended position untilfemoral component 142 is able to roll up and over inflection point 158.

As the knee joint enters a state of flexion, as shown in FIG. 28,lateral condyle 150 of femoral component 142 rolls across posteriorportion 156 of lateral articulating surface 152. Posterior portion 156of lateral articulating surface 152 may be sloped or curved to drivelateral condyle 150 in a posterior direction across tibial component144. Because medial condyle 146 remains substantially in place on medialarticulating surface 148 (FIG. 26), posterior portion 156 of lateralarticulating surface 152 drives rotation of femoral component 142relative to tibial component 144.

Referring to FIGS. 29-31, yet another exemplary knee prosthesis 160 isshown. Knee prosthesis 160 may incorporate features of knee prosthesis40 of FIGS. 8-13, knee prosthesis 40′ of FIGS. 56 and 57, kneeprosthesis 70 of FIGS. 14-17, knee prosthesis 90 of FIGS. 18-19, kneeprosthesis 110 of FIGS. 20 and 21, knee prosthesis 110′ of FIGS. 22-24,and/or knee prosthesis 140 of FIGS. 25-28.

Femoral component 162 of knee prosthesis 160 includes medial and lateralcondyles 166, 168. Medial wall 184 of medial condyle 166 and lateralwall 186 of lateral condyle 168 cooperate to define a substantiallytriangular shaped opening 182 therebetween.

Tibial component 164 of knee prosthesis 160 includes medial and lateralarticulating surfaces 170, 172. Tibial eminence 174 extends from tibialcomponent 164 between articulating surfaces 170, 172. As shown in FIG.31, anterior portion 176 of tibial eminence 174 has a substantiallytriangular cross-section. As shown in FIG. 30, posterior portion 178 oftibial eminence 174 has a rounded cross-section. Transition portion 180of tibial eminence 174 extends between anterior portion 176 andposterior portion 178. Transition portion 180 provides for a gradualtransition between the substantially triangular cross-section ofanterior portion 176 and the rounded cross-section of posterior portion178. In an anterior to posterior direction, from anterior portion 176,to transition portion 180, to posterior portion 178, tibial eminence 174decreases in height H and flattens out (i.e., increases in radius ofcurvature). As a result, the sharp point on anterior portion 176 oftibial eminence 174 gradually fades away toward posterior portion 178 oftibial eminence 174.

With the knee joint in extension, as shown in FIG. 31, anterior portion176 of tibial eminence 174 conforms tightly to the shape of opening 182in femoral component 162. The close, constraining fit between femoralcomponent 162 and tibial component 164 prevents relative rotationbetween the components.

With the knee joint in flexion, as shown in FIG. 30, posterior portion178 of tibial eminence 174 avoids medial and lateral walls 184, 186, offemoral component 162. In this flexed position, the loose fit betweenfemoral component 162 and tibial component 164 enables natural rotationbetween the components. For example, femoral component 162 may be freeto rotate relative to tibial component 164 about axis A withoutimpinging on tibial eminence 174. The loose fit between femoralcomponent 162 and tibial component 164 may also be achieved bydecreasing the width and/or the medial-lateral radius of curvature ofmedial and lateral condyles 166, 168, in flexion, as discussed abovewith reference to FIG. 17.

As the knee joint reenters extension, as shown in FIG. 31, anteriorportion 176 of tibial eminence 174 may contact either or both walls 184,186. This contact between femoral component 162 and tibial component 164may center and align the components as they reenter extension. Forexample, medial and lateral walls 184, 186, will guide tibial eminence174 into opening 182 until medial and lateral condyles 166, 168, offemoral component 162 are spaced atop and evenly situated upon medialand lateral articulating surfaces 170, 172, of tibial component 164,respectively. In this manner, tibial eminence 174 cooperates with walls184, 186, to drive femoral component 162 into a centered or homeposition when the knee joint is in extension.

Referring next to FIGS. 32-37, yet another exemplary knee prosthesis 190is shown. Knee prosthesis 190 includes femoral component 200 (FIG. 34)and tibial component 202 (FIG. 32). Knee prosthesis 190 may incorporatefeatures of knee prosthesis 40 of FIGS. 8-13, knee prosthesis 40′ ofFIGS. 56 and 57, knee prosthesis 70 of FIGS. 14-17, knee prosthesis 90of FIGS. 18-19, knee prosthesis 110 of FIGS. 20 and 21, knee prosthesis110′ of FIGS. 22-24, knee prosthesis 140 of FIGS. 25-28, and/or kneeprosthesis 160 of FIGS. 29-31.

As shown in FIGS. 32 and 33, tibial component 202 of knee prosthesis 190includes lateral articulating surface 204 and medial articulatingsurface 206. Lateral articulating surface 204 may be formed in anydesired manner. For example, lateral articulating surface 204 may beflat, concave, or sloped. Medial articulating surface 206 includesconcave outer section 208 having a first radius of curvature and concaveinner section 210 having a second radius of curvature. In one exemplaryembodiment, and as shown in FIG. 33, the second radius of curvature ofconcave inner section 210 is substantially less than the first radius ofcurvature 208 of concave outer section 208. As a result, concave innersection 210 forms a depression in medial articulating surface 206relative to concave outer section 208.

As shown in FIGS. 34-37, femoral prosthesis 200 of knee prosthesis 190includes medial condyle 212 and lateral condyle 214. As shown, lateralcondyle 214 may be formed in a traditional manner and have asubstantially consistent radius of curvature. In contrast, medialcondyle 212 includes projection 216 that defines an area of increasedthickness on the posterior portion of lateral condyle 214. In ananterior plane (FIG. 35), medial and lateral condyles 212, 214, havesubstantially similar cross-sections. In a more posterior plane (FIG.36), projection 216 extends from medial condyle 212 such that medialcondyle 212 is substantially increased in thickness compared to lateralcondyle 214. In a further posterior plane (FIG. 37), the thickness ofmedial condyle 212 is decreased slightly, but projection 216 stillprovides medial condyle 212 with an increased thickness over lateralcondyle 214.

In use, medial condyle 212 of femoral component 200 is designed toconform with medial articulating surface 206 of tibial component 202.For example, in extension, medial condyle 212 contacts shallow, outerarticulating portion 208 of medial articulating surface 206 of tibialcomponent 202. As the knee enters flexion, projection 216 of medialcondyle 212 enters concave inner surface 210 of medial articulatingsurface 206 of tibial component 202. Specifically, projection 216 issized such that the outer surface of projection 216 that is in contactwith concave inner surface 210 during knee joint flexion is highlyconforming to the wall defining concave inner surface 210 ofarticulating surface 206. As the knee joint continues through flexion,the interaction of projection 216 with concave inner surface 210 ofarticulating surface 206 may, depending on the configuration of concaveinner surface 210, cause a camming action that drives rotation offemoral component 200 relative to tibial component 202 about a mediallyoffset axis A. Specifically, projection 216 and inner surface 210 may bedesigned to drive rotation of lateral condyle 214 of femoral component200 about a medially offset axis that extends through concave innersurface 210.

Referring to FIGS. 38 and 39, yet another exemplary knee prosthesis 220is shown. Knee prosthesis 220 includes femoral component 222 and tibialcomponent 224. Knee prosthesis 220 may incorporate features of kneeprosthesis 40 of FIGS. 8-13, knee prosthesis 40′ of FIGS. 56 and 57,knee prosthesis 70 of FIGS. 14-17, knee prosthesis 90 of FIGS. 18-19,knee prosthesis 110 of FIGS. 20 and 21, knee prosthesis 110′ of FIGS.22-24, knee prosthesis 140 of FIGS. 25-28, knee prosthesis 160 of FIGS.29-31, and/or knee prosthesis 190 of FIGS. 32-37.

As shown in FIG. 38, femoral component 222 of knee prosthesis 220includes medial condyle 226, patello-femoral flange 228, a lateralcondyle (not shown), and crossbar 230 that extends between medialcondyle 226 and the lateral condyle. Tibial component 224 of kneeprosthesis 220 includes tibial eminence 232 that projects proximallyfrom the anterior portion of tibial component 224. The illustrativecrossbar 230 has a substantially circular cross-section and isconfigured to rest atop tibial eminence 232 of tibial component 224. Itis also within the scope of the present disclosure that crossbar 230and/or tibial eminence 232 may change shape and/or orientation in amedial-lateral direction to force the lateral condyle (not shown) offemoral component 222 to rotate about axis A. For example, crossbar 230and/or tibial eminence 232 may be conical in shape in the medial-lateraldirection. Tibial eminence 232 includes a substantially concave uppersurface 234 having a radius of curvature that is slightly less than theradius of crossbar 230.

With the knee joint in extension, as shown in FIG. 38, crossbar 230rests atop upper surface 234 of tibial eminence 232. To reduce wear oftibial eminence 232, crossbar 230 may hover slightly above the concaveupper surface 234 when the knee joint is in extension, abutting theanterior and posterior ends of upper surface 234 of tibial eminence 232only when necessary to limit anterior and posterior movement of tibia 12relative to femur 10. It is also within the scope of the presentdisclosure that crossbar 230 may fit snugly against tibial eminence 232for more constraint against anterior and posterior movements. Inaddition to limiting anterior and posterior movements of tibia 12relative to femur 10 when the knee joint is in extension, crossbar 230and tibial eminence 232 may also cooperate to limit rotation of tibia 12relative to femur 10.

As the knee enters flexion, as shown in FIG. 39, crossbar 230 separatesfrom upper surface 234 of tibial eminence 232. In this flexed position,femoral component 222 and tibial component 224 may move relative to oneanother in a natural, unobstructed manner. For example, the remainingligaments in the knee joint may drive rotation of femoral component 222relative to tibial component 224.

Referring to FIGS. 40-44, yet another exemplary knee prosthesis 238 isshown. Knee prosthesis 238 includes tibial component 240 (FIG. 40) andfemoral component 242 (FIG. 41). Knee prosthesis 238 may incorporatefeatures of knee prosthesis 40 of FIGS. 8-13, knee prosthesis 40′ ofFIGS. 56 and 57, knee prosthesis 70 of FIGS. 14-17, knee prosthesis 90of FIGS. 18-19, knee prosthesis 110 of FIGS. 20 and 21, knee prosthesis110′ of FIGS. 22-24, knee prosthesis 140 of FIGS. 25-28, knee prosthesis160 of FIGS. 29-31, knee prosthesis 190 of FIGS. 32-37, and/or kneeprosthesis 220 of FIGS. 38 and 39.

As shown in FIGS. 40 and 42, tibial component 240 of knee prosthesis 238includes medial and lateral articulating surfaces 244, 246. In a coronalplane, medial articulating surface 244 is more concave than lateralarticulating surface 246. While medial articulating surface 244 forms asubstantially concave surface, lateral articulating surface 246 forms asubstantially planar surface that slants downwardly in a medialdirection toward tibial eminence 248. For example, tibial component 240has a height H₁ along its lateral edge and a height H₂ that is less thanheight H₁ near tibial eminence 248. Lateral articulating surface 246also forms a generally arcuate path 247 about a medially offset axis A.Tibial component 240 may include posterior cutout 249 that is sized toreceive the retained posterior cruciate ligament.

As shown in FIGS. 41 and 42, femoral component 242 of knee prosthesis238 includes medial condyle 250 and lateral condyle 252. Themedial-lateral radius of curvature of medial condyle 250 issubstantially similar to the medial-lateral radius of curvature ofmedial articulating surface 244 of tibial component 240. Lateral condyle252 has an articulating surface that is slanted, with or without aslightly concave curvature, in a manner that allows the articulatingsurface of lateral condyle 252 to maintain contact with lateralarticulating surface 246 of tibial component 240.

When the knee joint is in an extended position, as shown in FIG. 42, thelateral height H₁ of lateral articulating surface 246 may exceed themedial height H₂ of lateral articulating surface 246. In thisembodiment, femoral component 242 may be biased medially toward tibialeminence 248 and toward the medially offset axis A. In other words, thetall lateral edge of tibial component 240 (along lateral height H₁) mayconstrain lateral movement of femoral component 242 relative to tibialcomponent 240. As shown in FIG. 42, the central height H₃ of lateralarticulating surface 246 exceeds the central height H₄ of medialarticulating surface 248 to further bias femoral component 242 mediallytoward the medially offset axis A. It is also within the scope of thepresent disclosure, as shown in FIG. 42A, that the central height H₃′ oflateral articulating surface 246′ may be approximately equal to thecentral height H₄′ of medial articulating surface 248′.

As the knee joint enters into flexion, femoral component 242 will rollback in a posterior direction. As shown in FIGS. 43 and 44, the lateralheight H₁ of lateral articulating surface 246 may decrease in aposterior direction (i.e. posterior to section line 42-42 of FIG. 40)such that femoral component 242 is less constrained against lateralmovement in the flexed position (FIGS. 43 and 44) than in the extendedposition (FIG. 42). This transition may occur gradually, with lateralarticulating surface 246 gradually decreasing in slope until reaching asubstantially horizontal surface or a slightly concave surface, as shownin FIG. 44.

Referring next to FIGS. 45 and 46, yet another exemplary knee prosthesis260 is shown. Knee prosthesis 260 includes femoral component 262 andtibial component 264. Knee prosthesis 260 may incorporate features ofknee prosthesis 40 of FIGS. 8-13, knee prosthesis 40′ of FIGS. 56 and57, knee prosthesis 70 of FIGS. 14-17, knee prosthesis 90 of FIGS.18-19, knee prosthesis 110 of FIGS. 20 and 21, knee prosthesis 110′ ofFIGS. 22-24, knee prosthesis 140 of FIGS. 25-28, knee prosthesis 160 ofFIGS. 29-31, knee prosthesis 190 of FIGS. 32-37, knee prosthesis 220 ofFIGS. 38 and 39, and/or knee prosthesis 238 of FIGS. 40-44.

Tibial component 264 of knee prosthesis 260 includes projection 266extending upwardly therefrom between medial articulating surface 268 andan opposing lateral articulating surface (not shown). Projection 266includes convex recess 270 formed therein.

Femoral component 262 of knee prosthesis 260 includes patello-femoralflange 272, medial condyle 274, and a lateral condyle (not shown).Crossbar 276 extends between medial condyle 274 and the lateral condyleof femoral component 262. The illustrative crossbar 276 has asubstantially circular cross-section and is sized for substantiallyconforming receipt within recess 270 of projection 266. It is alsowithin the scope of the present disclosure that projection 266 and/orcrossbar 276 may change shape and/or orientation in a medial-lateraldirection to force the lateral condyle (not shown) of femoral component262 to rotate about axis A.

With the knee joint in extension, as shown in FIG. 45, crossbar 276 isreceived within recess 270 of projection 266 in a substantiallyconforming relationship. Projection 66 abuts crossbar 276 to preventanterior movement of tibia 12 relative to femur 10.

As the knee joint reaches a state of flexion, as shown in FIG. 46,crossbar 276 disengages from projection 270. In this flexed position,femoral component 262 and tibial component 264 may move relative to oneanother in a natural, unobstructed manner. For example, the remainingligaments in the knee joint may drive rotation of femoral component 262relative to tibial component 264.

Referring next to FIGS. 47-50, yet another exemplary knee prosthesis 280is shown. Knee prosthesis 280 includes femoral component 282 and tibialcomponent 284. Knee prosthesis 280 may incorporate features of kneeprosthesis 40 of FIGS. 8-13, knee prosthesis 40′ of FIGS. 56 and 57,knee prosthesis 70 of FIGS. 14-17, knee prosthesis 90 of FIGS. 18-19,knee prosthesis 110 of FIGS. 20 and 21, knee prosthesis 110′ of FIGS.22-24, knee prosthesis 140 of FIGS. 25-28, knee prosthesis 160 of FIGS.29-31, knee prosthesis 190 of FIGS. 32-37, knee prosthesis 220 of FIGS.38 and 39, knee prosthesis 238 of FIGS. 40-44, and/or knee prosthesis260 of FIGS. 45 and 46.

Femoral component 282 of knee prosthesis 280 includes lateral condyle288 and projection 286 extending from a lateral-most side of lateralcondyle 288. Tibial component 284 of knee prosthesis 280 includeslateral articulating surface 292 and recess 290. Projection 286 offemoral component 282 is sized and shaped for receipt within recess 290of tibial component 284.

With the knee joint in extension, as shown in FIG. 48, projection 286 isreceived within recess 290 to limit movement of femur 10 relative totibia 12. However, as the knee joint enters flexion, projection 286exits from recess 290, allowing femoral component 282 and tibialcomponent 284 to move relative to one another in a natural, unobstructedmanner.

Referring next to FIGS. 51-53, still yet another exemplary kneeprosthesis 300 is shown. Knee prosthesis 300 includes femoral component302 and tibial component 304. Knee prosthesis 300 may incorporatefeatures of knee prosthesis 40 of FIGS. 8-13, knee prosthesis 40′ ofFIGS. 56 and 57, knee prosthesis 70 of FIGS. 14-17, knee prosthesis 90of FIGS. 18-19, knee prosthesis 110 of FIGS. 20 and 21, knee prosthesis110′ of FIGS. 22-24, knee prosthesis 140 of FIGS. 25-28, knee prosthesis160 of FIGS. 29-31, knee prosthesis 190 of FIGS. 32-37, knee prosthesis220 of FIGS. 38 and 39, knee prosthesis 238 of FIGS. 40-44, kneeprosthesis 260 of FIGS. 45 and 46, and/or knee prosthesis 280 of FIGS.47-50.

Knee prosthesis 300 may be substantially similar to knee prosthesis 280of FIGS. 47-50. However, unlike knee prosthesis 280 of FIGS. 47-50, kneeprosthesis 300 of FIGS. 51-53 includes a plurality of projections 306extending from lateral condyle 308 of femoral component 302 and aplurality of recesses 310 formed in lateral articulating surface 312 oftibial component 304. By providing a plurality of projections 306 andcorresponding recesses 310, knee prosthesis may lock in place in theextended position as long as any one of the projections 306 engages anadjacent recess 310. Therefore, knee prosthesis 300 may provide someflexibility in the relative positions of femoral component 302 andtibial component 304, while still achieving a stable extended position.

Referring finally to FIGS. 54 and 55, still yet another exemplary kneeprosthesis 320 is shown. Knee prosthesis 320 includes femoral component322 and tibial component 324. Knee prosthesis 320 may incorporatefeatures of knee prosthesis 40 of FIGS. 8-13, knee prosthesis 40′ ofFIGS. 56 and 57, knee prosthesis 70 of FIGS. 14-17, knee prosthesis 90of FIGS. 18-19, knee prosthesis 110 of FIGS. 20 and 21, knee prosthesis110′ of FIGS. 22-24, knee prosthesis 140 of FIGS. 25-28, knee prosthesis160 of FIGS. 29-31, knee prosthesis 190 of FIGS. 32-37, knee prosthesis220 of FIGS. 38 and 39, knee prosthesis 238 of FIGS. 40-44, kneeprosthesis 260 of FIGS. 45 and 46, knee prosthesis 280 of FIGS. 47-50,and/or knee prosthesis 300 of FIGS. 51-53.

Femoral component 322 of knee prosthesis 320 includes medial condyle 326and a lateral condyle (not shown). As shown in FIG. 54, medial condyle326 includes a substantially concave anterior portion 328 and asubstantially convex posterior portion 330. It is within the scope ofthe present disclosure that the lateral condyle (not shown) may beshaped as shown in FIG. 54, while medial condyle 326 may be entirelyconvex. It is also within the scope of the present disclosure that boththe lateral condyle (not shown) and medial condyle 326 may be shaped asshown in FIG. 54.

Tibial component 324 of knee prosthesis 320 includes medial articulatingsurface 332 and a corresponding lateral articulating surface (notshown). Medial articulating surface 332 has a substantially convexanterior portion 334 and a substantially concave posterior portion 336.Convex anterior portion 334 of medial articulating surface 332 of tibialcomponent 324 corresponds in curvature to concave anterior portion 328of medial condyle 326 of femoral component 322. Similarly, concaveposterior portion 336 of medical articulating surface 332 of tibialcomponent 324 corresponds in curvature to convex posterior portion 330of medial condyle 326 of femoral component 322.

With the knee joint in extension, as shown in FIG. 54, femoral component322 bears primarily against convex anterior portion 334 of tibialcomponent 324, with concave anterior portion 328 of medial condyle 326resting against convex anterior portion 334 of medial articulatingsurface 332. These surfaces cooperate to limit movement anteriormovement of tibia 12 relative to femur 10. As a result, knee prosthesis320 provides additional stability to the knee joint when the knee jointis in extension.

As the knee joint enters flexion, as shown in FIG. 55, concave anteriorportion 328 of medial condyle 236 disengages convex anterior portion 334of tibial component 324, allowing the remaining ligaments in the kneejoint to drive rotation of femoral component 322 relative to tibialcomponent 324. Femoral component 322 bears primarily against concaveposterior portion 336 of tibial component 324, with convex posterorportion 330 of medial condyle 326 resting against concave posteriorportion 336 of medial articulating surface 332.

As discussed above, it is within the scope of the present disclosure tocombine features of knee prosthesis 40 of FIGS. 8-13, knee prosthesis40′ of FIGS. 56 and 57, knee prosthesis 70 of FIGS. 14-17, kneeprosthesis 90 of FIGS. 18-19, knee prosthesis 110 of FIGS. 20 and 21,knee prosthesis 110′ of FIGS. 22-24, knee prosthesis 140 of FIGS. 25-28,knee prosthesis 160 of FIGS. 29-31, knee prosthesis 190 of FIGS. 32-37,knee prosthesis 220 of FIGS. 38 and 39, knee prosthesis 238 of FIGS.40-44, knee prosthesis 260 of FIGS. 45 and 46, knee prosthesis 280 ofFIGS. 47-50, knee prosthesis 300 of FIGS. 51-53, and/or knee prosthesis320 of FIGS. 54 and 55. Specifically, it is within the scope of thepresent disclosure to combine an intercondylar feature of one of thedisclosed knee prostheses with a condylar feature of another one of thedisclosed knee prostheses. Also, it is within the scope of the presentdisclosure to combine an anterior stabilizing feature of one of thedisclosed knee prostheses with a rotation-driving feature of another oneof the disclosed knee prostheses. For example, an exemplary kneeprosthesis may include the anterior stabilizing feature of kneeprosthesis 220 of FIGS. 38 and 39 (i.e., crossbar 230 and tibialeminence 232) and the rotation-driving feature of knee prosthesis 140 ofFIGS. 27 and 28 (i.e., tibial component 144 having a concave anteriorsection 154 and a concave posterior section 156 separated by inflectionpoint 158).

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. A knee prosthesis that is configured toarticulate between an extended position and a flexed position, the kneeprosthesis comprising: a femoral component including a medial condylehaving a medial wall and a lateral condyle having a lateral wall,wherein the medial and lateral walls come to a point and define atriangular shaped opening therebetween; and a tibial componentincluding: a medial surface sized to receive the medial condyle of thefemoral component; a lateral surface sized to receive the lateralcondyle of the femoral component; and a central eminence extendingproximally from the tibial component and configured to project betweenthe medial and lateral walls, the central eminence having an anteriorportion with flat surfaces forming a triangular cross-section that comesto a point and is configured to engage the triangular shaped opening andprevent relative rotation between the tibial and femoral components inthe extended position.
 2. The knee prosthesis of claim 1, wherein thecentral eminence includes: the anterior portion projecting between themedial and lateral walls in the extended position; and a posteriorportion configured to project between the medial and lateral walls inthe flexed position.
 3. The knee prosthesis of claim 2, wherein theanterior portion of the central eminence conforms tightly to thetriangular shaped opening in the extended position, and the posteriorportion of the central eminence loosely fits between the medial andlateral walls in the flexed position.
 4. The knee prosthesis of claim 3,wherein the posterior portion has a rounded cross-section.
 5. The kneeprosthesis of claim 4, wherein the central eminence graduallytransitions between the triangular cross-section and the roundedcross-section.
 6. The knee prosthesis of claim 3, wherein the medial andlateral walls are flat.
 7. The knee prosthesis of claim 3, wherein thecentral eminence has a decreasing height in an anterior to posteriordirection.
 8. The knee prosthesis of claim 7, wherein the centraleminence flattens in the anterior to posterior direction.
 9. The kneeprosthesis of claim 3, wherein the central eminence has a proximal endspaced from the femoral component in both the extended position and theflexed position.
 10. The knee prosthesis of claim 3, wherein the kneeprosthesis transitions from the extended position to the flexed positionbetween 10° and 30° of knee flexion, wherein the extended position ismore constrained than the flexed position.
 11. The knee prosthesis ofclaim 1, wherein a radius of curvature of one or both of the medial andlateral condyles decreases in size in an anterior to posteriordirection.
 12. The knee prosthesis of claim 1, wherein a width of themedial and lateral condyles decreases in size in an anterior toposterior direction.
 13. A knee prosthesis that articulates between anextended position and a flexed position, the extended position definedas including full extension up to 20° of knee flexion, the kneeprosthesis comprising: a femoral component including a medial condylehaving an inner medial wall and a lateral condyle having an innerlateral wall, the inner medial and lateral walls being flat to define atriangular shaped opening therebetween; and a tibial componentincluding: a medial surface configured for contact with at least aportion of the medial condyle of the femoral component; a lateralsurface configured for contact with at least a portion of the lateralcondyle of the femoral component; and a central eminence extendingproximally from the tibial component and projecting between the medialand lateral condyles of the femoral component in both the extendedposition and the flexed position, the central eminence having lesscontact with the inner medial and lateral walls when the knee prosthesisis in the flexed position than when the knee prosthesis is in theextended position such that the femoral and tibial components are moreconstrained, due to contact between the central eminence and the innermedial and lateral walls, against movement relative to each other whenthe knee prosthesis is in the extended position than when the kneeprosthesis is in the flexed position; wherein the central eminence hasan anterior portion including flat surfaces coming to a point andforming a triangular cross-section to engage the triangular shapedopening and prevent relative rotation between the tibial and femoralcomponents in the extended position.
 14. The knee prosthesis of claim13, wherein a posterior portion of the central eminence has a roundedcross-section, and wherein the central eminence gradually transitionsbetween the triangular cross-section and the rounded cross-section. 15.The knee prosthesis of claim 13, wherein the central eminence has adecreasing height in an anterior to posterior direction, and wherein thecentral eminence flattens in the anterior to posterior direction. 16.The knee prosthesis of claim 13, wherein the central eminence has aproximal end spaced from the femoral component in both the extendedposition and the flexed position.
 17. The knee prosthesis of claim 13,wherein the movement of the femoral and tibial components relative toeach other includes a rotational movement of the femoral componentrelative to the tibial component about an axis that is medially offsetfrom a center of the knee prosthesis, and the medial and lateralcondyles of the femoral component and the medial and lateral surfaces ofthe tibial component continue to drive rotation of the femoral componentrelative to the tibial component about the axis as the knee prosthesisarticulates from the extended position to the flexed position.
 18. Theknee prosthesis of claim 13, wherein the movement of the femoral andtibial components relative to each other includes at least one of: ananterior movement of the tibial component relative to the femoralcomponent; and a lateral movement of the femoral component relative tothe tibial component; and whereby the knee prosthesis resists themovement to a greater extent when the knee prosthesis is in the extendedposition than when the knee prosthesis is in the flexed position. 19.The knee prosthesis of claim 13, wherein: the inner medial wall of themedial condyle and the inner lateral wall of the lateral condyle come toa point to define the triangular shaped opening.